Earth boring cutter employing helical teeth

ABSTRACT

An earth bit includes an earth bit body and a lug and cutting cone carried by the earth bit body, wherein the cutting cone is rotatably mounted to the lug. A plurality of cutters are carried by the earth bit body, wherein the cutters include a cutter body and a plurality of curved teeth extending between opposed ends of the cutter body. The curved teeth are positioned so that one end of a tooth overlaps an opposed end of an adjacent tooth. The curved teeth of a first cutter extend in a direction around its corresponding cutter body and the curved teeth of a second cutter extend in an opposed direction around its corresponding cutter body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to cutters for earth bits.

2. Description of the Related Art

An earth bit is commonly used to bore holes into a formation. Such holes may be bored for many different reasons, such as drilling for oil, minerals and geothermal steam. There are several different types of earth bits that are used to bore holes. One type is a rotary earth bit and, in a typical setup, it includes three earth bit cutting cones rotatably mounted to a corresponding lug. The lugs are mounted on an earth bit body and, as the earth bit body is rotated in the bore hole, the earth bit cutting cones rotate in response to contacting the formation.

Another type of earth bit is a rolling cutter earth bit which typically includes a number of saddles carried by an earth bit body. A cutter is coupled with the earth bit body by rotatably mounting it to a saddle. Each cutter includes a number of teeth for boring into the formation. Examples of rolling cutter earth bits are disclosed in U.S. Pat. Nos. 3,444,939, 4,040,493, 4,161,225, 4,167,980, 4,393,949 and 5,456,328.

Most of these rolling cutter earth bits include cutters which are designed to bore through hard or medium hard formations, instead of soft formations such as soft limestone and soft-to-medium shale. Further, most of these rolling cutter earth bits include cutters which generate smaller cuttings. These rolling cutter earth bits typically include cutters which experience a significant amount of tracking, wherein the teeth of one cutter will follow in the path of the teeth of another cutter. It is desirable to reduce the amount of tracking because tracking reduces the operating life of the cutters and undesirably reduces the drilling efficiency of the earth bit.

Hence, there is a need for a rolling cutter earth bit for boring through soft formations, wherein the rolling cutter earth bit includes cutters which experience less tracking. Further, there is a need for a rolling cutter earth bit which includes cutters that generate larger cuttings when boring through soft formations.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a cutter, which includes a cutter body having opposed openings, and a plurality of curved teeth extending around the outer periphery, and between opposed ends, of the cutter body. The curved teeth have a curved edge, and a curved leading face that curves as it extends between opposed ends of the cutter body.

The cutter can include many other features. For example, in some embodiments, the curved teeth are positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth.

In some embodiments, the opposed ends of each curved tooth have different dimensions from each other. In some embodiments, the curved teeth include a curved leading face that curves as it extends between opposed ends of the cutter body. The plurality of curved teeth can include at least one curved tooth having first and second tooth portions spaced apart from each other. In some embodiments, the plurality of curved teeth includes first and second notched curved teeth. The notches of the first and second notched curved teeth can be offset from each other. In some embodiments, the plurality of curved teeth includes an unnotched curved tooth.

The invention provides an earth bit, which includes an earth bit body and a first cutter rotatably mounted to the earth bit body with a first saddle. The first cutter includes a cutter body, and a first plurality of curved teeth extending in a direction around the outer periphery, and between opposed ends, of the cutter body. The curved teeth are positioned so that one end of a curved tooth overlaps an opposed end of an adjacent curved tooth.

The earth bit can include many other features. For example, in some embodiments, the dimensions of a curved tooth at its end surface are smaller than the dimensions of the curved tooth at its opposed end surface. The curved teeth can include a curved edge and a curved face that curves as it extends away from the curved edge. In some embodiments, the first plurality of curved teeth includes at least one curved tooth having first and second tooth portions spaced apart from each other.

In one embodiment, the earth bit further includes a second cutter rotatably mounted to the earth bit body with a second saddle. The second cutter includes a cutter body and a second plurality of curved teeth extending between opposed ends and in an opposed direction around the outer periphery of the cutter body. The curved teeth of the second cutter are positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth. In some embodiments, the number of curved teeth of the first and second cutters are the same. The first and second saddles can be offset from each other.

In some embodiments, the earth bit further includes a third cutter rotatably mounted to the earth bit body with a third saddle. The third cutter includes a cutter body and a third plurality of curved teeth extending between opposed ends and in the direction around the outer periphery of the cutter body. The curved teeth of the third cutter are positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth. In this embodiment, the second cutter is positioned between the first and third cutters.

The invention provides an earth bit, which includes an earth bit body, and a lug and cutting cone carried by the earth bit body, wherein the cutting cone is rotatably mounted to the lug. The earth bit includes a plurality of cutters carried by the earth bit body, wherein the cutters include a cutter body and a plurality of curved teeth extending between opposed ends of the cutter body. The curved teeth are positioned so that one end of a tooth overlaps an opposed end of an adjacent tooth. The curved teeth of a first cutter extend in a direction around its corresponding cutter body and the curved teeth of a second cutter extend in an opposed direction around its corresponding cutter body.

The earth bit can include many other features. For example, in some embodiments, a tooth of the first cutter includes first and second tooth portions spaced apart from each other. In some embodiments, the dimensions of a curved tooth of the first cutter at its opposed end surfaces are different.

In some embodiments, the earth bit includes a third cutter having teeth which extend in the same direction as the teeth of the first cutter, wherein the second cutter is positioned between the first and third cutters. In these embodiments, the second cutter is offset from the first and third cutters to reduce the amount of tracking experienced by the teeth of the cutters.

Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b and 1 c are perspective, side and end views, respectively, of a cutter having a frusto-conical cutter body and straight teeth.

FIG. 2 a is a perspective view of a cutter, in accordance with the invention, having unnotched curved teeth.

FIGS. 2 b and 2 c are opposed end views of the cutter of FIG. 2 a.

FIG. 2 d is a close-up end view of the cutter of FIG. 2 a.

FIGS. 3 a and 3 b are perspective and side views, respectively, of a cutter, in accordance with the invention, having notched curved teeth.

FIGS. 3 c and 3 d are opposed end views of the cutter of FIG. 3 a.

FIGS. 3 e and 3 f are close-up end and side views, respectively, of the cutter of FIG. 3 a.

FIGS. 4 a and 4 b are perspective and side views, respectively, of a cutter, in accordance with the invention, having notched curved teeth.

FIGS. 4 c and 4 d are opposed end views of the cutter of FIG. 4 a.

FIGS. 4 e and 4 f are close-up end and side views, respectively, of the cutter of FIG. 4 a.

FIGS. 5 a and 5 b are bottom perspective and bottom views, respectively, of an embodiment of a rolling cutter earth bit, in accordance with the invention.

FIGS. 6 a and 6 b are bottom perspective and bottom views, respectively, of another embodiment of a rolling cutter earth bit, in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a cutter, and an earth bit which employs the cutter, for boring through soft formations. The cutter, in accordance with the invention, includes teeth that generate large cuttings when boring through the soft formations. Further, the earth bit, in accordance with the invention, includes a plurality of such cutters positioned to reduce the amount of tracking experienced by the teeth of the cutters. The operating life of the cutters and the drilling efficiency of the earth bit both increase in response to reducing the amount of tracking experienced by the teeth. It should be noted that the cutters disclosed herein can be interchanged with other types of cutters, such as those used to bore through hard and medium hard formations (i.e. formations that are harder than soft limestone and soft-to-medium shale). Hence, the cutters of the earth bit are interchangeable so that the earth bit can be modified to improve its ability to bore through soft, medium hard and hard formations.

FIG. 1 a is a perspective view of a cutter 100 having a frusto-conical cutter body 101 and a straight tooth 103, and FIGS. 1 b and 1 c are side and end views, respectively, of cutter 100. In this embodiment, cutter 100 includes a central opening 102 which extends through cutter body 101 and between opposed ends 106 a and 106 b. Cutter body 101 has a smaller outer diameter at end 106 a than at end 106 b. In this way, cutter body 101 has a frusto-conical shape.

In this embodiment, central opening 102 has the same shape and dimension at ends 106 a and 106 b and is sized and shaped to receive a shaft (not shown), so that cutter 100 can be rotatably mounted to an earth bit. Cutter 100 can be rotatably mounted to the earth bit in many different ways. In some embodiments, the earth bit includes a saddle and shaft, and cutter 100 is rotatably mounted to the saddle by extending the shaft through central opening 102. The shaft extends through opposed ends of central opening 102. More information regarding earth bits is provided with FIGS. 5 a and 5 b and FIGS. 6 a and 6 b.

In this embodiment, straight tooth 103 extends along the outer periphery of cutter body 101 and between opposed ends 106 a and 106 b. In general, cutter 100 can include any number of straight teeth, but it includes thirteen straight teeth here for illustrative purposes. In some embodiments, the number of teeth of cutter 100 is in a range between about seven and nineteen because this number of teeth has been found to be useful when boring through soft formations, such as soft limestone and soft-to-medium shale. Further, this number of teeth is useful to generate cuttings of a desired size when boring through soft formations. Hence, the size of the cuttings can be controlled by controlling the number of teeth included with cutter 100.

In this embodiment, straight tooth 103 includes a flat face 104 and straight edge 105, wherein flat face 104 and straight edge 105 do not curve between ends 106 a and 106 b. In this way, tooth 103 is a straight tooth with a flat face. The flatness and straightness of flat face 104 and straight edge 105 can best be seen in the side and end views of FIGS. 1 b and 1 c, respectively. It should be noted that the length of straight tooth 103 typically corresponds with the length of straight edge 105. Hence, the length of straight tooth 103 increases and decreases as the length of straight edge 105 increases and decreases, respectively.

In this embodiment, straight tooth 103 includes opposed surfaces 116 a (FIG. 1 a) and 116 b (FIG. 1 b) positioned proximate to ends 106 a and 106 b, respectively. Flat face 104 and straight edge 105 do not curve between surfaces 116 a and 116 b. In this way, tooth 103 is a straight tooth with a flat face. In cutter 100, surfaces 116 a and 116 b have the same shape and dimensions, wherein the shape is triangular. The dimensions of surfaces 116 a and 116 b can be characterized in many different ways. In this embodiment, surfaces 116 a and 116 b have the same dimensions because they have the same areas. In particular, surface 116 a has the same area as surface 116 b.

In FIG. 1 c, a radial line 109 extends radially and outwardly from a center 108 of cutter body 101. Straight edge 105 extends between opposed ends 106 a and 106 b so that it is perpendicular to radial line 109. Further, straight edge 105 extends between opposed surfaces 116 a and 116 b so that it is perpendicular to radial line 109. Radial line 109 extends so that it bisects opposed surfaces 116 a and 116 b of straight tooth 103. Radial line 109 bisects surface 116 a because the shape and area of surface 116 a is the same on opposed sides of radial line 109. Further, radial line 109 bisects surface 116 b because the shape and area of surface 116 b is the same on opposed sides of radial line 109. Straight edge 105 bisects surfaces 116 a and 116 b because it is perpendicular to radial line 109, and tooth 103 is a straight tooth.

It should be noted that radial line 109 can be positioned, without changing its angle relative to cutter body 101 and center 108, at any location of cutter body 101 between surfaces 116 a and 116 b and intersect straight edge 105. For example, radial line 109 is shown as being proximate to surfaces 116 a and 116 b in FIG. 1 a, wherein it intersects straight edge 105 proximate to surfaces 116 a and 116 b. In this way, radial line 109 can intersect straight edge 105 at any position between surfaces 116 a and 116 b without changing its angle relative to cutter body 101 and center 108. Hence, the same radial line (i.e. radial lines oriented at the same angle) extends through the intersection of straight edge 105 with opposed surfaces 116 a and 116 b.

FIG. 2 a is a perspective view of a cutter 110, in accordance with the invention, and FIGS. 2 b and 2 c are opposed end views of cutter 110. Cutter 110 is similar to cutter 100 discussed above, and includes cutter body 101 with central opening 102. However, in accordance with the invention, cutter 110 includes an unnotched curved tooth 113 which extends in a direction 107 a between opposed ends 106 a and 106 b and along the outer periphery of cutter body 101. Direction 107 a is in a clockwise direction when looking towards end 106 a (FIG. 2 b) and direction 107 a is in a counterclockwise direction when looking towards end 106 b (FIG. 2 c). Cutter 110 can include any number of unnotched curved teeth, but it includes thirteen unnotched curved teeth here for illustrative purposes. In some embodiments, the number of unnotched curved teeth of cutter 110 is in a range between about seven and nineteen for reasons mentioned above.

In this embodiment, unnotched curved tooth 113 includes a curved face 114 and curved edge 115, wherein curved face 114 and curved edge 115 curve between ends 106 a and 106 b. Further, curved face 114 curves as it extends away from curved edge 115. In this way, curved tooth 113 is a curved tooth with a curved face. Hence, curved tooth 113 is not a straight tooth with a flat face, like tooth 103 discussed above. The curvature of curved face 114 and curved edge 115 can be seen in FIGS. 2 a, 2 b and 2 c. It should be noted that curved face 114 is a curved leading face because it engages the formation in response to the rotation of cutter 110 in direction 107 a.

In this embodiment, unnotched curved tooth 113 includes opposed surfaces 116 a (FIG. 2 b) and 116 b (FIG. 2 c) positioned proximate to ends 106 a and 106 b, respectively. Curved face 114 and curved edge 115 curve between surfaces 116 a and 116 b. In this way, tooth 113 is a curved tooth with a curved face. In cutter 110, surfaces 116 a and 116 b can have many different shapes, such as triangular. However, the shapes of surfaces 116 a and 116 b of cutter 110 are typically different from each other. For example, in one embodiment, surface 116 a is shaped like an equilateral triangle and surface 116 b is not shaped like an equilateral triangle. In another embodiment, surface 116 a is shaped like an isosceles triangle and surface 116 b is not shaped like an isosceles triangle. In one embodiment, surface 116 a is shaped like an equilateral triangle and surface 116 b is shaped like an isosceles or scalene triangle. In another embodiment, surface 116 a is shaped like an isosceles triangle and surface 116 b is shaped like an equilateral or scalene triangle. In this way, the shapes of surfaces 116 a and 116 b of cutter 110 are different from each other. It should be noted that, in FIGS. 2 b and 2 c, surfaces 116 a and 116 b are shaped like isosceles and scalene triangles, respectively.

The dimensions of surfaces 116 a and 116 b of cutter 110 are typically different from each other. As mentioned above, the dimensions of surfaces 116 a and 116 b can be characterized in many different ways. In this embodiment, surfaces 116 a and 116 b have different dimensions because they have different areas. In particular, surfaces 116 a and 116 b have different dimensions because surface 116 a has a smaller area than surface 116 b.

In FIG. 2 b and 2 c, radial lines 109 a and 109 b extend radially and outwardly from center 108 of cutter body 101, wherein radial lines 109 a and 109 b are proximate to ends 106 a and 106 b, respectively. Radial line 109 a extends so that it intersects the intersection of curved edge 115 and surface 116 a, and radial line 109 b extends so that it intersects the intersection of curved edge 115 and surface 116 b. Radial line 109 a extends so that it bisects surface 116 a (FIG. 2 b) because the shape and area of surface 116 a of tooth 113 is the same on opposed sides of radial line 109 a. Radial line 109 a bisects surface 116 a when surface 116 a has a shape like an equilateral or isosceles triangle. Radial line 109 b extends so that it does not bisect surface 116 b (FIG. 2 c) because the shape and area of surface 116 b of tooth 113 is not the same on opposed sides of radial line 109 b. Radial line 109 b extends so that it does not bisect surface 116 b when the shape of surface 116 b is not an equilateral or isosceles triangle. Radial line 109 b extends so that it does not bisect surface 116 b when the shape of surface 116 b is a scalene triangle. Hence, surface 116 a is symmetrical with radial line 109 a and surface 116 b is non-symmetrical with radial line 109 b.

In this embodiment, curved edge 115 curves between radial lines 109 a and 109 b. Curved edge 115 is curved so that radial lines 109 a and 109 b are at an angle θ₁ relative to each other, as seen in FIGS. 2 b and 2 c. Angle θ₁ is nonzero so that the same radial line does not extend through the intersections of curved edge 115 and opposed surfaces 116 a and 116 b, as with cutter 100.

Angle θ₁ can have many different angular values. For example, in one embodiment, angle θ₁ is less than about twenty degrees and, in another embodiment, angle θ₁ is less than about fifteen degrees. In one particular embodiment, angle θ₁ is between about two degrees and fifteen degrees. In another particular embodiment, angle θ₁ is between about five degrees and twenty degrees.

In general, the amount of curvature of tooth 113 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. Further, the amount of twist of tooth 113 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. As the amount of twist of tooth 113 increases and decreases, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of tooth 113 is adjustable in response to adjusting the magnitude of angle θ₁.

In general, the length of unnotched curved tooth 113 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The length of unnotched curved tooth 113 typically corresponds with the length of curved edge 115. The length of unnotched curved tooth 113 increases and decreases as the length of curved edge 115 increases and decreases, respectively. Hence, the length of curved edge 115 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively.

It should be noted that the curvature of unnotched curved tooth 113, for a constant angle θ₁, typically increases and decreases as the length of curved edge 115 decreases and increases, respectively. Further, the curvature of unnotched curved tooth 113, for a constant length of curved edge 115, typically increases and decreases as angle θ₁ increases and decreases, respectively.

FIG. 2 d is a close-up end view of cutter 110 looking towards end 106 a, as in FIG. 2 b. In accordance with the invention, the unnotched curved teeth of cutter 110 overlap each other. The unnotched curved teeth of cutter 110 can overlap each other in many different ways. As shown in FIG. 2 d, cutter 110 includes unnotched curved teeth 113 a and 113 b, which are adjacent to each other. Curved teeth 113 a and 113 b are the same as curved tooth 113 discussed above. Curved tooth 113 a includes curved face 114 a and curved edge 115 a, and curved tooth 113 b includes curved face 114 b and curved edge 115 b. Radial line 109 a extends between center 108 of cutter body 101 and the intersection of surface 116 a of tooth 113 a and curved edge 115 a. Further, radial line 109 b extends between center 108 of cutter body 101 and the intersection of surface 116 b of curved tooth 113 a and curved edge 115 a. A radial line 109 c extends between center 108 of cutter body 101 and the intersection of surface 116 a of tooth 113 b and curved edge 115 b. As mentioned above, radial lines 109 a and 109 b are at angle θ₁ relative to each other. Further, radial lines 109 a and 109 c are at an angle θ₂ relative to each other. It should be noted that radial lines 109 a and 109 c are proximate to end 106 a, and radial line 109 b is proximate to end 106 b.

In accordance with the invention, curved teeth 113 a and 113 b overlap each other. The overlapping of curved teeth 113 a and 113 b can be characterized in many different ways. In this embodiment, curved teeth 113 a and 113 b overlap each other because angle θ₁ is greater than angle θ₂. Angle θ₁ is greater than angle θ₂ so that a curved edge portion 117 b of curved edge 115 b overlaps a curved edge portion 117 a of curved edge 115 a. Curved edge portions 117 a and 117 b extend between radial lines 109 b and 109 c. Hence, curved teeth 113 a and 113 b overlap each other because curved edge portions of curved edges 115 a and 115 b overlap each other. In this way, cutter 110 includes unnotched curved teeth which overlap each other.

Angle θ₁ is greater than angle θ₂ so that a curved surface portion 118 b of curved surface 114 b overlaps a curved surface portion 118 a of curved surface 114 a. Curved surface portions 118 a and 118 b extend between radial lines 109 b and 109 c. Curved surface portion 118 a is bounded between radial lines 109 b and 109 c and curved edge portion 117 a and surface 116 b of tooth 113 a. Further, curved surface portion 118 b is bounded between radial lines 109 b and 109 c and curved edge portion 117 b and surface 116 a of tooth 113 b. Hence, curved teeth 113 a and 113 b overlap each other because curved surface portions of curved surfaces 114 a and 114 b overlap each other. In this way, cutter 110 includes unnotched curved teeth which overlap each other.

The amount of overlap of curved teeth 113 a and 113 b can be adjusted in many different ways. For example, the difference between angles θ₁ and θ₂ can be increased by increasing the curvature of curved surface 114 a. Further, the difference between angles θ₁ and θ₂ can be increased by increasing the curvature of curved edge 115 a. The difference between angles θ₁ and θ₂ can be decreased by decreasing the curvature of curved surface 114 a. Further, the difference between angles θ₁ and θ₂ can be decreased by decreasing the curvature of curved edge 115 a. In this way, the amount of overlap of curved teeth 113 a and 113 b can be adjusted in response to adjusting the curvature of curved surface 114 a and curved edge 115 a.

It should be noted that curved teeth 113 a and 113 b do not overlap each other when angle θ₁ is less than angle θ₂. Further, curved teeth 113 a and 113 b do not substantially overlap each other when angles θ₁ and θ₂ are substantially the same. In some embodiments, cutter 110 provides an improved cutting efficiency when teeth 113 a and 113 b do not overlap each other, and when curved teeth 113 a and 113 b do not substantially overlap each other. For example, in some embodiments, cutter 110 provides an improved cutting efficiency when angle θ₁ is between zero degrees and five degrees less than angle θ₂. In some embodiments, cutter 110 provides an improved cutting efficiency when angle θ₁ is between zero degrees and ten degrees less than angle θ₂. In some embodiments, cutter 110 provides an improved cutting efficiency when angle θ₁ is between zero degrees and fifteen degrees less than angle θ₂.

In the embodiment of FIG. 2 d, curved teeth 113 a and 113 b overlap each other so that the intersection of curved edge 115 a and surface 116 b of curved tooth 113 a leads the intersection of curved edge 115 b and surface 116 a of curved tooth 113 b in response to rotating cutter body 101 in direction 107 a. In this way, the intersection of curved edge 115 a and surface 116 b of curved tooth 113 a impacts the formation before the intersection of curved edge 115 b and surface 116 a of curved tooth 113 b in response to rotating cutter body 101 in direction 107 a. Further, curved edge portion 117 a impacts the formation before curved edge portion 117 b, and curved surface portion 118 a impacts the formation before curved surface portion 118 b.

Cutter 110 provides many advantages. For example, the curved teeth of cutter 110 overlap each other so that cutter 110 is more stable in response to cutter body 101 rotating in direction 107 a. Cutter 110 is more stable in response to cutter body 101 rotating in direction 107 a because at least one curved tooth of cutter 110 will always be in contact with the formation. In this way, the curved teeth will hold cutter body 101 to the formation so that it vibrates less. Further, the curved teeth of cutter 110 will remain in contact with the formation for a longer amount of time than a straight tooth, such as tooth 103. The curved teeth of cutter 110 will remain in contact with the formation for a longer amount of time than a straight tooth because a curved tooth is generally longer than a straight tooth. Also, a curved tooth is longer than a straight tooth so that its number of impacts per revolution of cutter body 101 is reduced. For example, a single curved tooth will experience one impact per revolution, but a straight tooth may experience multiple impacts per revolution.

Another advantage provided by cutter 110 is that the curved teeth are not torqued upwardly in response to engaging the formation. It is known that straight teeth will be lifted up in response to engaging the formation, which causes them to experience an upwardly directed force that torques them. It is undesirable to torque the teeth of a cutter in this manner because they can fracture and become detached from cutter body 101.

Another advantage provided by cutter 110 is that curved teeth 113 each have a wider base which is blended into cutter body 101 for additional strength. The base of a curved tooth also facilitates the removal of cuttings from between adjacent curved teeth and reduces the likelihood of pack-off. A cutting is a portion of the formation that has been cut by the cutter. Pack-off occurs when a portion of the cutting is cut from the formation and becomes lodged between adjacent teeth. Pack-off will result in an effectively shortened tooth which will reduce the penetration rate of the tooth into the formation.

FIG. 3 a is a perspective view of a cutter 120, in accordance with the invention, and FIGS. 3 b and 3 c are end and side views, respectively, of cutter 120. Cutter 120 is similar to cutter 110 discussed above, and includes cutter body 101 with central opening 102. However, in accordance with the invention, cutter 120 includes a notched curved tooth 123 which extends in direction 107 a between opposed ends 106 a and 106 b and along the outer periphery of cutter body 101. Cutter 120 can include any number of notched curved teeth, but it includes thirteen notched curved teeth here for reasons discussed above. In some embodiments, the number of notched curved teeth of cutter 120 is in a range between about seven and nineteen. It should be noted that all the teeth included with cutter 120 can be notched curved teeth, or one or more of the teeth included with cutter 120 can be notched curved teeth. In this embodiment, cutter 120 includes one tooth (i.e. tooth 113) that is unnotched, and several curved teeth that are notched.

In accordance with the invention, notched curved tooth 123 includes first and second tooth portions 126 and 127 with a notch 128 positioned between them. In this way, first and second tooth portions 126 and 127 are spaced apart from each other by notch 128. Hence, tooth 123 is a notched tooth and is not an unnotched tooth like teeth 103 and 113 discussed above. Teeth 103 and 113 are unnotched teeth because they do not include first and second tooth portions spaced apart from each other with a notch. It should be noted that first and second tooth portions 126 and 127, as well as notch 128, extend around cutter body 101 in the same direction as notched curved tooth 123. Hence, first and second tooth portions 126 and 127 and notch 128 extend in direction 107 a because notched curved tooth 123 extends in direction 107 a.

In this embodiment, notched curved tooth 123 includes curved face 114 and curved edge 115 (FIG. 3 b), wherein curved face 114 and curved edge 115 curve between ends 106 a and 106 b. In this way, notched curved tooth 123 is a curved tooth with a curved face. Hence, notched curved tooth 123 is not a straight tooth with a flat face like tooth 103 discussed above. The curvature of curved face 114 and curved edge 115 can be seen in FIGS. 3 a, 3 b and 3 c. It should be noted that curved face 114 and curved edge 115 extend through first and second tooth portions 126 and 127. Hence, tooth portions 126 and 127 both include portions of curved face 114 and curved edge 115.

In this embodiment, unnotched curved tooth 123 includes opposed surfaces 116 a (FIG. 3 c) and 116 b (FIG. 3 d) positioned proximate to ends 106 a and 106 b, respectively. Curved face 114 and curved edge 115 curve between surfaces 116 a and 116 b. In this way, tooth 123 is a curved tooth with a curved face. In cutter 120, surfaces 116 a and 116 b can have many different shapes, such as triangular. However, the shapes of surfaces 116 a and 116 b of cutter 120 are typically different from each other. For example, in one embodiment, surface 116 a is shaped like an equilateral triangle and surface 116 b is not shaped like an equilateral triangle. In another embodiment, surface 116 a is shaped like an isosceles triangle and surface 116 b is not shaped like an isosceles triangle. In one embodiment, surface 116 a is shaped like an equilateral triangle and surface 116 b is shaped like an isosceles or scalene triangle. In another embodiment, surface 116 a is shaped like an isosceles triangle and surface 116 b is shaped like an equilateral or scalene triangle. In this way, the shapes of surfaces 116 a and 116 b of cutter 120 are different from each other. It should be noted that, in FIGS. 3 c and 3 d, surfaces 116 a and 116 b are shaped like isosceles and scalene triangles, respectively.

The dimensions of surfaces 116 a and 116 b of cutter 120 are typically different from each other. As mentioned above, the dimensions of surfaces 116 a and 116 b can be characterized in many different ways. In this embodiment, surfaces 116 a and 116 b have different dimensions because they have different areas. In particular, surface 116 a has a smaller area than surface 116 b.

It should be noted that surfaces 116 a and 116 b are included with first and second tooth portions 126 and 127, respectively. As shown in FIGS. 3 a, 3 c and 3 d, first tooth portion 126 includes a surface 116 c which is opposed to surface 116 a, and second tooth portion 127 includes a surface 116 d which is opposed to surface 116 b. Hence, first tooth portion 126 extends between surfaces 116 a and 116 c and second tooth portion 127 extends between surfaces 116 b and 116 d. Further, notch 128 extends between surfaces 116 c and 116 d. Curved face 114 and curved edge 115 of first tooth portion 126 extend between surfaces 116 a and 116 c, and curved face 114 and curved edge 115 of second tooth portion 127 extend between surfaces 116 b and 116 d.

It should be noted that, in this embodiment, surfaces 116 c and 116 d have different dimensions. The dimensions of surfaces 116 c and 116 d can be characterized in many different ways, such as those discussed above with surfaces 116 a and 116 b. In this embodiment, surfaces 116 c and 116 d have different dimensions because they have different areas. In particular, surface 116 c has a smaller area than surface 116 d. In other embodiments, surfaces 116 c and 116 d have the same dimensions wherein surfaces 116 c and 116 d have the same areas.

It should also be noted that, in this embodiment, surfaces 116 c and 116 d can have the same or different shapes. The shapes of surfaces 116 c and 116 d can be characterized in many different ways, such as those discussed above with surfaces 116 a and 116 b. In this embodiment, surfaces 116 c and 116 d have the same shape because they are both isosceles triangles. In other embodiments, surfaces 116 c and 116 d have the same shape because they are both equilateral or scalene triangles. In other embodiments, surfaces 116 c and 116 d have different shapes. For example, in one embodiment, surfaces 116 c and 116 d are shaped like equilateral and isosceles triangles, respectively.

In FIGS. 3 c and 3 d, radial lines 109 a and 109 b extend radially and outwardly from center 108 of cutter body 101, wherein radial lines 109 a and 109 b are proximate to ends 106 a and 106 b, respectively. Radial line 109 a extends so that it intersects the intersection of curved edge 115 and surface 116 a, and radial line 109 b extends so that it intersects the intersection of curved edge 115 and surface 116 b. Radial line 109 a extends so that it bisects surface 116 a (FIG. 3 c) because the shape and area of surface 116 a of tooth 123 is the same on opposed sides of radial line 109 a. Radial line 109 b extends so that it does not bisect surface 116 b (FIG. 3 d) because the shape and area of surface 116 b of tooth 123 is not the same on opposed sides of radial line 109 b. Hence, surface 116 a is symmetrical with radial line 109 a and surface 116 b is non-symmetrical with radial line 109 b.

In this embodiment, curved edge 115 (FIG. 3 b) of tooth portions 126 and 127 curves between radial lines 109 a and 109 b. Curved edge 115 is curved so that radial lines 109 a and 109 b are at an angle θ₁ relative to each other, as seen in FIGS. 3 c and 3 d. Angle θ₁ is nonzero so that the same radial line does not extend through the intersections of curved edge 115 and opposed surfaces 116 a and 116 b, as with cutter 100.

Angle θ₁ can have many different angular values, such as those mentioned in more detail above with cutter 110. In general, the amount of curvature of tooth 123 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. Further, the amount of twist of tooth 123 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. As the amount of twist of tooth 123 increases and decreases, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of tooth 123 is adjustable in response to adjusting the magnitude of angle θ₁.

The amount of curvature of first and second tooth portions 126 and 127 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 of first and second tooth portions 126 and 127 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. Further, the amount of twist of first and second tooth portions 126 and 127 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. As the amount of twist of first and second tooth portions 126 and 127 increase and decrease, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of first and second tooth portions 126 and 127 is adjustable in response to adjusting the magnitude of angle θ₁.

In general, the length of notched curved tooth 123 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The length of notched curved tooth 123 typically corresponds with the length of curved edge 115. The length of notched curved tooth 123 increases and decreases as the length of curved edge 115 increases and decreases, respectively. Hence, the length of curved edge 115 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively.

It should be noted that the curvature of notched curved tooth 123, for a constant angle θ₁, typically increases and decreases as the length of curved edge 115 decreases and increases, respectively. Further, the curvature of notched curved tooth 123, for a constant length of curved edge 115, typically increases and decreases as angle θ₁ increases and decreases, respectively.

FIG. 3 e is a close-up end view of cutter 120 looking towards end 106 a, as in FIG. 3 b. In accordance with the invention, the curved teeth of cutter 120 overlap each other. It should be noted that the notched and unnotched curved teeth of cutter 120 generally overlap each other. The curved teeth of cutter 120 can overlap each other in many different ways. As shown in FIG. 3 e, cutter 120 includes notched curved teeth 123 a, 123 b and 123 c, which are adjacent to each other. Notched curved tooth 123 b is positioned between notched curved teeth 123 a and 123 c. Curved teeth 123 a, 123 b and 123 c are the same as curved tooth 123 discussed above.

Curved tooth 123 a includes first and second tooth portions 126 a and 127 a with a curved face 114 a and curved edge 115 a. Curved face 114 a and curved edge 115 a extend through tooth portions 126 a and 127 a. Curved tooth 123 b includes first and second tooth portions 126 b and 127 b with a curved face 114 b and curved edge 115 b. Curved face 114 b and curved edge 115 b extend through tooth portions 126 b and 127 b. Curved tooth 123 c includes first and second tooth portions 126 c and 127 c with a curved face 114 c and curved edge 115 c. Curved face 114 c and curved edge 115 c extend through tooth portions 126 c and 127 c.

Radial line 109 a extends between center 108 of cutter body 101 and the intersection of surface 116 a of tooth 123 b and curved edge 115 b. Further, radial line 109 b extends between center 108 of cutter body 101 and the intersection of surface 116 b of curved tooth 123 b and curved edge 115 b. A radial line 109 c extends between center 108 of cutter body 101 and the intersection of surface 116 a of tooth 123 c and curved edge 115 c. As mentioned above, radial lines 109 a and 109 b are at angle θ₁ relative to each other. Further, radial lines 109 a and 109 c are at an angle θ₂ relative to each other. It should be noted that radial lines 109 a and 109 c are proximate to end 106 a, and radial line 109 b is proximate to end 106 b.

In accordance with the invention, notched curved teeth 123 b and 123 c overlap each other. The overlapping of notched curved teeth 123 b and 123 c can be characterized in many different ways. In this embodiment, curved teeth 123 b and 123 c overlap each other because angle θ₁ is greater than angle θ₂. Angle θ₁ is greater than angle θ₂ so that a curved edge portion 117 c of curved edge 115 c overlaps curved edge portion 117 b of curved edge 115 b. Curved edge portions 117 b and 117 c extend between radial lines 109 b and 109 c. Hence, curved teeth 123 b and 123 c overlap each other because curved edge portions of curved edges 115 b and 115 c overlap each other. In this way, cutter 120 includes unnotched curved teeth which overlap each other.

Angle θ₁ is greater than angle θ₂ so that a curved surface portion 118 c of curved surface 114 c overlaps curved surface portion 118 b of curved surface 114 b. Curved surface portions 118 b and 118 c extend between radial lines 109 b and 109 c. Curved surface portion 118 b is bounded between radial lines 109 b and 109 c and curved edge portion 117 b and surface 116 b of tooth 123 b. Further, curved surface portion 118 c is bounded between radial lines 109 b and 109 c and curved edge portion 117 c and surface 116 c of tooth 113 c. Hence, curved teeth 123 b and 123 c overlap each other because curved surface portions of curved surfaces 114 b and 114 c overlap each other. In this way, cutter 120 includes notched curved teeth which overlap each other.

The amount of overlap of curved teeth 123 b and 123 c can be adjusted in many different ways. For example, the difference between angles θ₁ and θ₂ can be increased by increasing the curvature of curved surface 114 b of tooth portion 127 b. Further, the difference between angles θ₁ and θ₂ can be increased by increasing the curvature of curved edge 115 b of tooth portion 127 b. The difference between angles θ₁ and θ₂ can be decreased by decreasing the curvature of curved surface 114 b of tooth portion 127 b. Further, the difference between angles θ₁ and θ₂ can be decreased by decreasing the curvature of curved edge 115 b of tooth portion 127 b. In this way, the amount of overlap of curved teeth 123 b and 123 c can be adjusted in response to adjusting the curvature of curved surface 114 b and curved edge 115 b of tooth portion 127 b.

It should be noted that curved teeth 123 b and 123 c do not overlap each other when angle θ₁ is less than angle θ₂. Further, curved teeth 123 b and 123 c do not substantially overlap each other when angles θ₁ and θ₂ are substantially the same. In some embodiments, cutter 120 provides an improved cutting efficiency when teeth 123 a and 123 b do not overlap each other, and when curved teeth 123 a and 123 b do not substantially overlap each other. For example, in some embodiments, cutter 120 provides an improved cutting efficiency when angle θ₁ is between zero degrees and five degrees less than angle θ₂. In some embodiments, cutter 120 provides an improved cutting efficiency when angle θ₁ is between zero degrees and ten degrees less than angle θ₂. In some embodiments, cutter 120 provides an improved cutting efficiency when angle θ₁ is between zero degrees and fifteen degrees less than angle θ₂.

In the embodiment of FIG. 3 e, curved teeth 123 b and 123 c overlap each other so that the intersection of curved edge 115 b and surface 116 b of curved tooth 123 b leads the intersection of curved edge 115 c and surface 116 a of curved tooth 123 c in response to rotating cutter body 101 in direction 107 a. In this way, the intersection of curved edge 115 b and surface 116 b of curved tooth 123 b impacts the formation before the intersection of curved edge 115 c and surface 116 a of curved tooth 123 c in response to rotating cutter body 101 in direction 107 a.

FIG. 3 f is a close-up side view of cutter 120, as seen in FIG. 3 b. In accordance with the invention, the notches of each adjacent notched curved tooth are offset from each other. The notches of each adjacent notched curved tooth can be offset from each other in many different ways. For example, the notches of each adjacent curved tooth can be staggered relative to each other. When the notches of adjacent curved teeth are staggered relative to each other, they are a different distance away from end 106 a. Further, when the notches of adjacent curved teeth are staggered relative to each other, they are a different distance from end 106 b.

For example, in this embodiment, cutter 120 includes notched curved teeth 123 a, 123 b and 123 c, wherein notched curved tooth 123 c is positioned between notched curved teeth 123 a and 123 b. Notched curved teeth 123 a, 123 b and 123 c include notches 128 a, 128 b and 128 c, respectively. Notches 128 a, 128 b and 128 c are positioned distances D₁, D₂ and D₃, respectively, from end 106 b, wherein distance D₁ is less than distance D₂ and distance D₂ is less than distance D₃. In this way, notches 128 a, 128 b and 128 c are different distances from end 106 b so that they are staggered relative to each other.

It should be noted that distances D₁, D₂ and D₃ can correspond to many different distances between end 106 b and corresponding notches 128 a, 128 b and 128 c. For example, in this embodiment, distance D₁ is the distance between end 106 b and the intersection of surface 116 d and curved edge 115 a of tooth portion 127 a of tooth 123 a. Distance D₂ is the distance between end 106 b and the intersection of surface 116 d and curved edge 115 b of tooth portion 127 b of tooth 123 b. Further, distance D₃ is the distance between end 106 b and the intersection of surface 116 d and curved edge 115 c of tooth portion 127 c of tooth 123 c. It should be noted that three different notch positions for the staggered notches are shown in this example for illustrative purposes. However, cutter 120 generally includes two or more different notch positions for the staggered notches.

Cutter 120 provides many advantages, such as those mentioned above with cutter 110. For example, the curved teeth of cutter 120 overlap each other so that cutter 120 is more stable in response to cutter body 101 rotating in direction 107 a. Another advantage provided by cutter 120 is that the notches allow material from the cuttings to flow therethrough, which reduces the likelihood of pack-off and increases the drilling efficiency. In general, the drilling efficiency increases when cutter 120 cuts through more material per rotation. Further, the notches are staggered relative to each other, which facilitates the removal of material from between adjacent teeth and reduces the amount of pack-off.

FIG. 4 a is a perspective view of a cutter 130, in accordance with the invention, and FIGS. 4 b and 4 c are end and side views, respectively, of cutter 130. Cutter 130 is similar to cutters 110 and 120 discussed above, and includes cutter body 101 with central opening 102. However, in accordance with the invention, cutter 130 includes a notched curved tooth 133 which extends in a direction 107 b between opposed ends 106 a and 106 b and along the outer periphery of cutter body 101. Direction 107 b is opposed to direction 107 a. Hence, direction 107 b is clockwise if direction 107 a is counterclockwise, and direction 107 b is counterclockwise if direction 107 a is clockwise.

Cutter 130 can include any number of notched curved teeth, but it includes thirteen notched curved teeth here for reasons discussed above. In some embodiments, the number of notched curved teeth of cutter 130 is in a range between about seven and nineteen. It should be noted that all the teeth included with cutter 130 can be notched curved teeth, or one or more of the teeth included with cutter 130 can be notched curved teeth. In this embodiment, cutter 130 includes one tooth (i.e. tooth 113) that is unnotched, and several curved teeth that are notched.

In accordance with the invention, notched curved tooth 133 includes first and second tooth portions 136 and 137 with a notch 138 positioned between them. In this way, first and second tooth portions 136 and 137 are spaced apart from each other by notch 138. Hence, tooth 133 is a notched tooth and is not an unnotched tooth like teeth 103 and 113 discussed above. Teeth 103 and 113 are unnotched teeth because they do not include first and second tooth portions spaced apart from each other with a notch. It should be noted that first and second tooth portions 136 and 137, as well as notch 138, extend around cutter body 101 in the same direction as notched curved tooth 133. Hence, first and second tooth portions 136 and 137 and notch 138 extend in direction 107 b because notched curved tooth 133 extends in direction 107 b.

In this embodiment, notched curved tooth 133 includes curved face 114 and curved edge 115 (FIG. 4 b), wherein curved face 114 and curved edge 115 curve between ends 106 a and 106 b. In this way, notched curved tooth 133 is a curved tooth with a curved face. Hence, notched curved tooth 133 is not a straight tooth with a flat face, like tooth 103 discussed above. The curvature of curved face 114 and curved edge 115 can be seen in FIGS. 4 a, 4 b and 4 c. It should be noted that curved face 114 and curved edge 115 extend through first and second tooth portions 136 and 137. Hence, tooth portions 136 and 137 both include portions of curved face 114 and curved edge 115.

In this embodiment, unnotched curved tooth 133 includes opposed surfaces 116 a (FIG. 4 c) and 116 b (FIG. 4 d) positioned proximate to ends 106 a and 106 b, respectively. Curved face 114 and curved edge 115 curve between surfaces 116 a and 116 b. In this way, tooth 133 is a curved tooth with a curved face. In cutter 130, surfaces 116 a and 116 b can have many different shapes, such as triangular. However, the shapes of surfaces 116 a and 116 b of cutter 130 are typically different from each other. For example, in one embodiment, surface 116 a is shaped like an equilateral triangle and surface 116 b is not shaped like an equilateral triangle. In another embodiment, surface 116 a is shaped like an isosceles triangle and surface 116 b is not shaped like an isosceles triangle. In one embodiment, surface 116 a is shaped like an equilateral triangle and surface 116 b is shaped like an isosceles or scalene triangle. In another embodiment, surface 116 a is shaped like an isosceles triangle and surface 116 b is shaped like an equilateral or scalene triangle. In this way, the shapes of surfaces 116 a and 116 b of cutter 130 are different from each other. It should be noted that, in FIGS. 4 c and 4 d, surfaces 116 a and 116 b are shaped like isosceles and scalene triangles, respectively.

The dimensions of surfaces 116 a and 116 b of cutter 130 are typically different from each other. As mentioned above, the dimensions of surfaces 116 a and 116 b can be characterized in many different ways. In this embodiment, surfaces 116 a and 116 b have different dimensions because they have different areas. In particular, surface 116 a has a smaller area than surface 116 b.

It should be noted that surfaces 116 a and 116 b are included with first and second tooth portions 136 and 137, respectively. As shown in FIGS. 4 a, 4 c and 4 d, first tooth portion 146 includes surface 116 c which is opposed to surface 116 a, and second tooth portion 137 includes surface 116 d which is opposed to surface 116 b. Hence, first tooth portion 136 extends between surfaces 116 a and 116 c and second tooth portion 137 extends between surfaces 116 b and 116 d. Further, notch 138 extends between surfaces 116 c and 116 d. Curved face 114 and curved edge 115 of first tooth portion 136 extend between surfaces 116 a and 116 c, and curved face 114 and curved edge 115 of second tooth portion 137 extend between surfaces 116 b and 116 d.

It should be noted that, in this embodiment, surfaces 116 c and 116 d have different dimensions. The dimensions of surfaces 116 c and 116 d can be characterized in many different ways, such as those discussed above with surfaces 116 a and 116 b. In this embodiment, surfaces 116 c and 116 d have different dimensions because they have different areas. In particular, surface 116 c has a smaller area than surface 116 d. In other embodiments, surfaces 116 c and 116 d have the same dimensions wherein surfaces 116 c and 116 d have the same areas.

It should also be noted that, in this embodiment, surfaces 116 c and 116 d can have the same or different shapes. The shapes of surfaces 116 c and 116 d can be characterized in many different ways, such as those discussed above with surfaces 116 a and 116 b. In this embodiment, surfaces 116 c and 116 d have the same shape because they are both isosceles triangles. In other embodiments, surfaces 116 c and 116 d have the same shape because they are both equilateral or scalene triangles. In other embodiments, surfaces 116 c and 116 d have different shapes. For example, in one embodiment, surfaces 116 c and 116 d are shaped like equilateral and isosceles triangles, respectively.

In FIGS. 4 c and 4 d, radial lines 109 a and 109 b extend radially and outwardly from center 108 of cutter body 101, wherein radial lines 109 a and 109 b are proximate to ends 106 a and 106 b, respectively. Radial line 109 a extends so that it intersects the intersection of curved edge 115 and surface 116 a, and radial line 109 b extends so that it intersects the intersection of curved edge 115 and surface 116 b. Radial line 109 a extends so that it bisects surface 116 a (FIG. 4 c) because the shape and area of surface 116 a of tooth 123 is the same on opposed sides of radial line 109 a. Radial line 109 b extends so that it does not bisect surface 116 b (FIG. 4 d) because the shape and area of surface 116 b of tooth 123 is not the same on opposed sides of radial line 109 b. Hence, surface 116 a is symmetrical with radial line 109 a and surface 116 b is non-symmetrical with radial line 109 b.

In this embodiment, curved edge 115 (FIG. 4 b) of tooth portions 136 and 137 curves between radial lines 109 a and 109 b. Curved edge 115 is curved so that radial lines 109 a and 109 b are at an angle θ₁ relative to each other, as seen in FIGS. 4 c and 4 d. Angle θ₁ is nonzero so that the same radial line does not extend through the intersections of curved edge 115 and opposed surfaces 116 a and 116 b, as with cutter 100. Angle θ₁ can have many different angular values. In general, the amount of curvature of tooth 133 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. Further, the amount of twist of tooth 133 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. As the amount of twist of tooth 133 increases and decreases, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of tooth 133 is adjustable in response to adjusting the magnitude of angle θ₁.

The amount of curvature of first and second tooth portions 136 and 137 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The amount of curvature of curved face 114 and curved edge 115 of first and second tooth portions 136 and 137 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. Further, the amount of twist of first and second tooth portions 136 and 137 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. As the amount of twist of first and second tooth portions 136 and 137 increase and decrease, the amount of twist of curved face 114 and curved edge 115 increases and decreases, respectively. In this way, the amount of curvature and twist of first and second tooth portions 136 and 137 is adjustable in response to adjusting the magnitude of angle θ₁.

In general, the length of notched curved tooth 133 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively. The length of notched curved tooth 133 typically corresponds with the length of curved edge 115. The length of notched curved tooth 133 increases and decreases as the length of curved edge 115 increases and decreases, respectively. Hence, the length of curved edge 115 increases and decreases as the magnitude of angle θ₁ increases and decreases, respectively.

It should be noted that the curvature of notched curved tooth 133, for a constant angle θ₁, typically increases and decreases as the length of curved edge 115 decreases and increases, respectively. Further, the curvature of notched curved tooth 133, for a constant length of curved edge 115, typically increases and decreases as angle θ₁ increases and decreases, respectively.

FIG. 4 e is a close-up end view of cutter 130 looking towards end 106 a, as in FIG. 4 b. In accordance with the invention, the curved teeth of cutter 130 overlap each other. It should be noted that the notched and unnotched curved teeth of cutter 130 generally overlap each other. The curved teeth of cutter 130 can overlap each other in many different ways. As shown in FIG. 4 e, cutter 130 includes notched curved teeth 133 a and 133 b which are adjacent to each other. Curved teeth 133 a and 133 b are the same as curved tooth 133 discussed above.

Curved tooth 133 a includes first and second tooth portions 136 a and 137 a with curved face 114 a and curved edge 115 a. Curved face 114 a and curved edge 115 a extend through tooth portions 136 a and 137 a. Curved tooth 133 b includes first and second tooth portions 136 b and 137 b with curved face 114 b and curved edge 115 b. Curved face 114 b and curved edge 115 b extend through tooth portions 136 b and 137 b.

Radial line 109 a extends between center 108 of cutter body 101 and the intersection of surface 116 a of tooth 133 a and curved edge 115 a. Further, radial line 109 b extends between center 108 of cutter body 101 and the intersection of surface 116 b of curved tooth 133 a and curved edge 115 a. Radial line 109 c extends between center 108 of cutter body 101 and the intersection of surface 116 a of tooth 133 b and curved edge 115 b. As mentioned above, radial lines 109 a and 109 b are at angle θ₁ relative to each other, and radial lines 109 a and 109 c are at an angle θ₂ relative to each other. It should be noted that radial lines 109 a and 109 c are proximate to end 106 a, and radial line 109 b is proximate to end 106 b.

In accordance with the invention, notched curved teeth 133 a and 133 b overlap each other. The overlapping of notched curved teeth 133 a and 133 b can be characterized in many different ways. In this embodiment, curved teeth 133 a and 133 b overlap each other because angle θ₁ is greater than angle θ₂. Angle θ₁ is greater than angle θ₂ so that a curved edge portion 117 b of curved edge 115 b overlaps a curved edge portion 117 a of curved edge 115 a. Curved edge portions 117 a and 117 b extend between radial lines 109 b and 109 c. Hence, curved teeth 133 a and 133 b overlap each other because curved edge portions of curved edges 115 a and 115 b overlap each other. In this way, cutter 130 includes unnotched curved teeth which overlap each other.

Angle θ₁ is greater than angle θ₂ so that curved surface portion 118 b of curved surface 114 b overlaps curved surface portion 118 a of curved surface 114 a. Curved surface portions 118 a and 118 b extend between radial lines 109 b and 109 c. Curved surface portion 118 a is bounded between radial lines 109 b and 109 c and curved edge portion 117 a and surface 116 b of tooth 133 a. Further, curved surface portion 118 b is bounded between radial lines 109 b and 109 c and curved edge portion 117 b and surface 116 a of tooth 113 b. Hence, curved teeth 133 a and 133 b overlap each other because curved surface portions of curved surfaces 114 a and 114 b overlap each other. In this way, cutter 130 includes notched curved teeth which overlap each other.

The amount of overlap of curved teeth 133 a and 133 b can be adjusted in many different ways. For example, the difference between angles θ₁ and θ₂ can be increased by increasing the curvature of curved surface 114 a of tooth portion 137 a. Further, the difference between angles θ₁ and θ₂ can be increased by increasing the curvature of curved edge 115 a of tooth portion 137 a. The difference between angles θ₁ and θ₂ can be decreased by decreasing the curvature of curved surface 114 a of tooth portion 137 a. Further, the difference between angles θ₁ and θ₂ can be decreased by decreasing the curvature of curved edge 115 a of tooth portion 137 a. In this way, the amount of overlap of curved teeth 133 a and 133 b can be adjusted in response to adjusting the curvature of curved surface 114 a and curved edge 115 a of tooth portion 137 a.

It should be noted that curved teeth 133 a and 133 b do not overlap each other when angle θ₁ is less than angle θ₂. Further, curved teeth 133 a and 133 b do not substantially overlap each other when angles θ₁ and θ₂ are substantially the same. In some embodiments, cutter 130 provides an improved cutting efficiency when teeth 133 a and 133 b do not overlap each other, and when curved teeth 133 a and 133 b do not substantially overlap each other. For example, in some embodiments, cutter 130 provides an improved cutting efficiency when angle θ₁ is between zero degrees and five degrees less than angle θ₂. In some embodiments, cutter 130 provides an improved cutting efficiency when angle θ₁ is between zero degrees and ten degrees less than angle θ₂. In some embodiments, cutter 130 provides an improved cutting efficiency when angle θ₁ is between zero degrees and fifteen degrees less than angle θ₂.

In the embodiment of FIG. 4 e, curved teeth 133 a and 133 b overlap each other so that the intersection of curved edge 115 a and surface 116 b of curved tooth 133 a leads the intersection of curved edge 115 b and surface 116 a of curved tooth 133 b in response to rotating cutter body 101 in direction 107 b. In this way, the intersection of curved edge 115 a and surface 116 b of curved tooth 133 a impacts the formation before the intersection of curved edge 115 b and surface 116 a of curved tooth 133 b in response to rotating cutter body 101 in direction 107 b.

FIG. 4 f is a close-up side view of cutter 130, as seen in FIG. 4 b. In accordance with the invention, the notches of each adjacent notched curved tooth are offset from each other. The notches of each adjacent notched curved tooth can be offset from each other in many different ways. For example, the notches of each adjacent curved tooth can be staggered relative to each other. When the notches of adjacent curved teeth are staggered relative to each other, they are a different distance away from end 106 a. Further, when the notches of adjacent curved teeth are staggered relative to each other, they are a different distance from end 106 b.

For example, in this embodiment, cutter 130 includes notched curved teeth 133 a, 133 b and 133 c, wherein notched curved tooth 133 c is positioned between notched curved teeth 133 a and 133 b. Notched curved teeth 133 a, 133 b and 133 c include notches 138 a, 138 b and 138 c, respectively. Notches 138 a, 138 b and 138 c are positioned distances D₁, D₂ and D₃, respectively, from end 106 b, wherein distance D₁ is less than distance D₂ and distance D₂ is less than distance D₃. In this way, notches 138 a, 138 b and 138 c are different distances from end 106 b so that they are staggered relative to each other.

It should be noted that distances D₁, D₂ and D₃ can correspond to many different distances between end 106 b and corresponding notches 138 a, 138 b and 138 c. For example, in this embodiment, distance D₁ is the distance between end 106 b and the intersection of surface 116 d and curved edge 115 a of tooth portion 137 a of tooth 133 a. Distance D₂ is the distance between end 106 b and the intersection of surface 116 d and curved edge 115 b of tooth portion 137 b of tooth 133 b. Further, distance D₃ is the distance between end 106 b and the intersection of surface 116 d and curved edge 115 c of tooth portion 137 c of tooth 133 c. It should be noted that three different notch positions for the staggered notches are shown in this example for illustrative purposes. However, cutter 130 generally includes two or more different notch positions for the staggered notches.

Cutter 130 provides many advantages, such as those mentioned above with cutters 110 and 120. For example, the curved teeth of cutter 130 overlap each other so that cutter 130 is more stable in response to cutter body 101 rotating in direction 107 a. Another advantage provided by cutter 130 is that the notches allow material from the cuttings to flow therethrough, which reduces the likelihood of pack-off and increases the drilling efficiency. Further, the notches are staggered relative to each other, which facilitates the removal of material from between adjacent teeth and reduces the amount of pack-off. Another advantage provided by cutter 120 is that the notches allow material from the cuttings to flow therethrough, which reduces the likelihood of pack-off

FIGS. 5 a and 5 b are bottom perspective and bottom views, respectively, of an earth bit 150, in accordance with the invention, which can carry the cutters discussed above. In this embodiment, earth bit 150 is embodied as a rolling cutter earth bit and includes an earth bit body 151 which carries saddles 152, 153, 154, 155 and 156. Earth bit 150 includes cutters 120 and 130, wherein cutter 120 is rotatably mounted to saddles 153 and 156 and cutter 130 is rotatably mounted to saddles 152, 154 and 155. Cutters 120 and 130 are discussed in more detail above. Saddles 152, 153, 154, 155 and 156 are positioned so that their longitudinal axis extends radially outwardly from a center 158 (FIG. 5 b) of earth bit body 151. The longitudinal axis of saddle 152 is indicated in FIGS. 5 a and 5 b and denoted as axis 169, wherein axis 169 extends through center 158. It should be noted that the cutter rotatably mounted to saddle 152 rotates about axis 169.

The amount of tracking experienced by the cutters of an earth bit is typically reduced by including cutters having different numbers of teeth. However, in accordance with the invention, the cutters of earth bit 150 experience less tracking, even when they have the same number of teeth. The cutters of earth bit 150 can experience less tracking even when they have the same number of teeth in many different ways.

In accordance with the invention, the saddles of earth bit 150 are positioned relative to each other to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 150. The saddles of earth bit 150 can be positioned relative to each other in many different ways to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 150. As best seen in FIG. 5 b, the saddles are offset so that they are positioned at various distances from center 158 of earth bit body 151.

For example, in this embodiment, saddles 153 and 155 are positioned closer to center 158 than saddles 152, 154 and 156 so that the cutters rotatably mounted to saddles 153 and 155 are closer to center 158 than the cutters rotatably mounted to saddles 152, 154 and 156. In particular, saddles 153 and 155 are positioned a radial distance from center 158, wherein the radial distance corresponds with the radius of a reference circle 157. Further, saddles 152, 154 and 156 are positioned a radial distance from center 158, wherein the radial distance corresponds with the radius of a reference circle 159. The radius of reference circle 157 is less than the radius of reference circle 159 so that saddles 153 and 155 are closer to center 158 than saddles 152, 154 and 156. In this way, saddles 153 and 155 are positioned closer to center 158 than saddles 152, 154 and 156. The radius of reference circle 157 is less than the radius of reference circle 159 so that the cutters rotatably mounted to saddles 153 and 155 are closer to center 158 than the cutters rotatably mounted to saddles 152, 154 and 156. In this way, the cutters rotatably mounted to saddles 153 and 155 are positioned closer to center 158 than the cutters rotatably mounted to saddles 152, 154 and 156.

In accordance with the invention, the types of cutters rotatably mounted in the saddles of earth bit 150 are selected to reduce the amount of tracking experienced by their teeth. The types of cutters rotatably mounted in the saddles of earth bit 150 can be selected in many different ways to reduce the amount of tracking experienced by their teeth. In this embodiment, saddle 153 is positioned between saddles 152 and 154. As mentioned above, cutter 130 is rotatably mounted with saddles 152 and 154, and cutter 120 is rotatably mounted with saddle 153. In this way, cutter 120 is positioned between two cutters 130. Cutter 120 includes teeth that curve in direction 107 a and cutter 130 includes teeth that curve in direction 107 b. Hence, the amount of tracking experienced by the teeth of the cutters rotatably mounted to saddles 152, 153 and 154 is reduced by positioning a cutter with teeth curving in one direction (i.e. direction 107 a) between two cutters with teeth curving in an opposed direction (i.e. direction 107 b). It should be noted that the amount of tracking experienced by the two cutters is reduced even when they both include the same or a different number of teeth.

In some embodiments, cutter 130 is rotatably mounted to saddle 153 and cutter 130 is rotatably mounted to saddles 152 and 154. In this way, the amount of tracking experienced by the teeth of the cutters rotatably mounted to saddles 152, 153 and 154 is reduced by positioning a cutter with teeth curving in one direction (i.e. direction 107 b) between two cutters with teeth curving in an opposed direction (i.e. direction 107 a).

Hence, in accordance with the invention, cutters 120 and 130 of earth bit 150 can each have the same number of teeth and still experience less tracking. In this particular embodiment, cutters 120 and 130 of earth bit 150 each have thirteen teeth. However, as mentioned above, cutters 120 and 130 can each include a number of teeth within a range of about seven to nineteen, wherein the number of teeth of cutters 120 and 130 are the same. Hence, cutter 120 includes eleven teeth if cutter 130 includes eleven teeth and cutter 120 includes fourteen teeth if cutter 130 includes fourteen teeth.

It should be noted that the cutters of earth bit 150 are interchangeable and replaceable with the cutters discussed herein. Hence, any of cutters 100, 110, 120 and 130 can be rotatably mounted to saddles 152, 153, 154, 155 and 156. The selection of which cutters are included with earth bit 150 depends on many different factors, such as the hardness of the formation it is desired to bore through. For example, cutter 100 and/or cutter 110 are typically selected when it is desired to bore through a hard or medium hard formation. Further, cutter 120 and/or cutter 130 are typically selected when it is desired to bore through a soft formation. In this way, the cutters of earth bit 100 are interchangeable and can be chosen in response to the type of formation it is desired to bore through.

FIGS. 6 a and 6 b are bottom perspective and bottom views, respectively, of an earth bit 160, in accordance with the invention, which can carry the cutters discussed above. In this embodiment, earth bit 160 is embodied as a rolling cutter earth bit and includes earth bit body 151 which carries saddles 152, 153, 154, 155 and 156, which are discussed above. Earth bit 160 includes cutters 120 and 130, wherein cutter 120 is rotatably mounted to saddles 153 and 156 and cutter 130 is rotatably mounted to saddles 152, 154 and 155. Cutters 120 and 130 are discussed in more detail above. Saddles 152, 153, 154, 155 and 156 are positioned so that their longitudinal axis extends radially outwardly from center 158 (FIG. 6 b) of earth bit body 151. The longitudinal axis of saddle 152 is indicated in FIGS. 6 a and 6 b and denoted as axis 169, wherein axis 169 extends through center 158. It should be noted that the cutter rotatably mounted to saddle 152 rotates about axis 169.

As mentioned above, the amount of tracking experienced by the cutters of an earth bit is typically reduced by including cutters having different numbers of teeth. However, in accordance with the invention, the cutters of earth bit 160 experience less tracking, even when they have the same number of teeth. The cutters of earth bit 160 can experience less tracking even when they have the same number of teeth in many different ways, such as those discussed above with earth bit 150.

In accordance with the invention, the saddles of earth bit 160 are positioned relative to each other to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 150. The saddles of earth bit 160 can be positioned relative to each other in many different ways to reduce the amount of tracking experienced by the teeth of the cutters of earth bit 160. As best seen in FIG. 6 b, the saddles are offset so that they are positioned at various distances from center 158 of earth bit body 151. More information about offsetting saddles of an earth bit is provided above with FIGS. 5 a and 5 b.

In this embodiment, the amount of tracking experienced by the teeth of the cutters of earth bit 100 is reduced by includes a cutting cone 161 rotatably mounted to a lug 162, wherein lug 162 is carried by earth bit body 151. Lug 162 and cutting cone 161 are positioned between saddles 152 and 156, wherein cutters 130 and 120 are rotatably mounted to saddles 152 and 156, respectively. In this way, lug 162 and cutting cone 161 are positioned between cutters 120 and 130. It should be noted that, in some embodiments, cutters 120 and 130 are rotatably mounted with saddles 152 and 156, respectively.

While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims. 

1. A cutter, comprising: a cutter body having opposed openings; and a plurality of curved teeth extending around the outer periphery of the cutter body and between opposed ends, wherein the curved teeth have a curved edge, and a curved leading face that curves as it extends between opposed ends of the cutter body.
 2. The cutter of claim 1, wherein the curved teeth are positioned so that an end of a curved tooth overlaps an opposed end of an adjacent curved tooth.
 3. The cutter of claim 1, wherein opposed ends of each curved tooth have different dimensions.
 4. The cutter of claim 1, wherein the plurality of curved teeth includes at least one curved tooth having first and second tooth portions spaced apart from each other.
 5. The cutter of claim 1, wherein the plurality of curved teeth includes first and second notched curved teeth.
 6. The cutter of claim 5, wherein the notches of the first and second notched curved teeth are offset from each other.
 7. The cutter of claim 5, wherein the plurality of curved teeth includes an unnotched curved tooth.
 8. An earth bit, comprising: an earth bit body; and a first cutter rotatably mounted to the earth bit body with a first saddle, the first cutter including a cutter body and a first plurality of curved teeth extending in a direction around the outer periphery of the cutter body and between opposed ends, the curved teeth being positioned so that one end of a curved tooth overlaps an opposed end of an adjacent curved tooth.
 9. The cutter of claim 8, wherein the dimensions of a curved tooth at its end surface are smaller than the dimensions of the curved tooth at its opposed end surface.
 10. The cutter of claim 8, wherein the curved teeth include a curved edge, and a curved face that curves as it extends away from the curved edge.
 11. The cutter of claim 8, wherein the first plurality of curved teeth includes at least one curved tooth having first and second tooth portions spaced apart from each other.
 12. The earth bit of claim 8, further including a second cutter rotatably mounted to the earth bit body with a second saddle, the second cutter including a cutter body; and a second plurality of curved teeth extending between opposed ends and in an opposed direction around the outer periphery of the cutter body, the curved teeth being positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth.
 13. The earth bit of claim 12, wherein the number of curved teeth of the first and second cutters are the same.
 14. The earth bit of claim 12, wherein the first and second saddles are offset from each other.
 15. The earth bit of claim 12, further including a third cutter rotatably mounted to the earth bit body with a third saddle, the third cutter including a cutter body; and a third plurality of curved teeth extending between opposed ends and in the direction around the outer periphery of the cutter body, the curved teeth being positioned so that one end of a curved tooth overlaps the opposed end of an adjacent curved tooth; wherein the second cutter is positioned between the first and third cutters.
 16. An earth bit, comprising: an earth bit body; a lug and cutting cone carried by the earth bit body, the cutting cone being rotatably mounted to the lug; and a plurality of cutters carried by the earth bit body, wherein the cutters include a cutter body and a plurality of curved teeth extending between opposed ends of the cutter body, the curved teeth being positioned so that one end of a tooth overlaps an opposed end of an adjacent tooth; wherein the curved teeth of a first cutter extend in a direction around its corresponding cutter body and the curved teeth of a second cutter extend in an opposed direction around its corresponding cutter body.
 17. The earth bit of claim 16, wherein a tooth of the first cutter includes first and second tooth portions spaced apart from each other.
 18. The cutter of claim 16, wherein the dimensions of a curved tooth of the first cutter at its opposed end surfaces are different from each other.
 19. The cutter of claim 16, further including a third cutter having teeth which extend in the same direction as the teeth of the first cutter, the second cutter being positioned between the first and third cutters.
 20. The cutter of claim 19, wherein the second cutter is offset from the first and third cutters. 